We have found that hydrogen peroxide (a tryptophan photoproduct) acts synergistically with near-ultraviolet (300-400nm) radiations and visible (400-500)nm radiations to produce aberrant genetic effects in bacteria and bacteriophage. We plan (1) to determine the precise wavelengths that optimally act synergistically to produce these aberrations (i.e., action spectrum analysis); (2) to identify the chromophore that is altered by the radiation; (3) to determine the role of hydrogen peroxide in its interaction with nucleic acid, protein or other bio-molecule that may be involved; (4) to determine the genetic consequences of this synergistic action; (5) since we know that this synergism may affect steps in the recombinational pathway, we hope to identify the precise molecular events; (6) to use this synergistic action as a probe to identify the precise role of recA gene products in consumating genetic recombination. Results from these experiments should give us a clearer understanding of the role of near-ultraviolet radiations in influencing genetic and cellular activities. BIBLIOGRAPHIC REFERENCES: McCormick, J.P., J.R. Fischer, J. P. Pachlatko, and A. Eisenstark. 1976. Characterization of a cell-lethal product from the photooxidation of tryptophan: hydrogen peroxide. Science 191: 468-469. Mackay, Donna, A. Eisenstark, R.B. Webb, and M.S. Brown. 1976. Action spectra for lethality in recombinationless strains of Salmonella typhimurium and Escherichia coli. Photochem. Photobiol. 24:337-343.